Telephone system



TELEPHONE SYSTEM Filed May 2, 1938 8 Sheets-Sheet l A. KEYSER ETAL TELEPHONE SYSTEM Filed May 2, 1938 Dec. 9, 1941.

8 Sheets-Sheet 2 INV ENT ORS ALFRED KEYSER GEORG ZAPF ATTORNEY.

Dec. 9, 19412 A. KEYSER ETAL TELEPHONE SYSTEM Filed May 2, 1938 8 Sheets-Sheei'l 3 'ueAq FIG. 2A

. lNvENToRs ALFRED KEYSER GEORG ZPF BY ya Pme ATrcDRNE-Y.

8 Sheets-Sheet 4 m .c U

INVENTORS ATTORNEY 9, 1941. A. KEYsER Erm.

TELEPHONE SYSTEM .v NB Nezllw mvzhw wtzW/Qzwmr E; y

A. KEYSER ETAL TELEPHONE SYSTEM Dec. 9, 1941.

A. KEYSER ET AL TELEPHONE SYSTEM 8 Sheets-Sheet 6 Filed May 2, 1938 bro INVENTORS ALFREQ KEYsER BY 66ans zAPF Dec. 9, 1941. A, KEYsER ETAL 2,265,235

`TELEPH0NE SYSTEM Filed May 2, 1938 8 Sheets-Sheet 7 Y INVENTORS ALFRED KEYSER GEoRG z'PF wf@ f l f ATTORNEY. l'

Patented Dec. 9, 1941 TELEPHONE SYSTEM Alfred Keyser, Berlin-Siemensstadt, Georg` Zapf,

Berlin-Charlottenburg, and

Walter Pinell,

Falkensee, near Berlin, Germany, assignors to Siemens 2 Halske Aktiengesellschaft, Wernerwerk, Slemensstadt, near Berlin, Germany Application May 2, 1938, Serial No. 205,480

In Germany May 5, 1937 .22 Claims.

m the calling subscribers disposal for setting up calls to the Wanted exchange.

vIn order to be able to utilize all the connecting paths over which a Wanted exchange can be reached, it is known for a hunting switch automatically to search for a free connecting line in another main trailic direction in the p event of the preferred connecting line outgoing in a particular main traiiic direction being engaged, the wanted call being also able to be established over the free connecting line.

Moreover, it has also been proposed that when establishing a call over one or more intermediate exchanges a connecting path established from one to another intermediate exchange should be released if all the outgoing connecting lines in the desired direction which can be reached over this intermediate exchange are engaged. The connection is then established automatically over another exchange.

The present invention now enables all the outgoing connecting paths in various main trailic directions which come into question for setting up a call to be utilized in that in the exchange (the starting exchange) from which the connecting paths outgoing in various trafiic directions are reached, switching means are provided which extend a call which can be set up over intermediate exchanges lying in different I vbut may be an intermediate exchange lying in the connecting path of the connection which has been established.

The connections are established in the shortm est time by using the arrangement according to the invention because the partial establishment of the connection to an intermediate exchange and the release of the latter when the further connecting lines extended from this exchange areblocked and the fresh establishment of a connection in another direction is prevented.

Moreover impulse repeaters, registers and the quired.

For characterizing the inaccessibility of the outgoing connecting lines from an intermediate exchange in a particular direction a bIOcked" signal is transmitted from the intermediate exchange back to the starting exchange.

According to the invention the connections are set up over secondary switches which calling stations when initiating calls connect to the connecting lines of these main trailic directions over which free outgoing lines from the intermediate exchanges are reached.

Under the iniluence of switching means controlled by the "blocked signal the secondary switches can only seize outgoing free connecting lines in a particular direction when a call is initiated.

By -using secondary switches which are preset the connecting path which can be used for a connection to be established can alwaysbe n prepared.

connection at the intermediate exchanges is aui tomatically switched through to the wanted terminal exchange. Ihis is preferably achieved by using a plurality of approaches to the outgoing connecting lines which are given diierent digit combinations in that when seizing one of these approaches a signal peculiar to the wanted exchange is transmitted to the next exchange.

In the drawings some embodiments of the invention are represented to which however the invention is not limited.

All details which are not absolutely necessary `for the understanding of the invention have been omitted. In the embodiments one-way connecting lines can also be used.

Fig. l shows diagrammatically and without circuit details a telephdne system having iive exchanges VStA, VStB, VStC, VStD and VStE.

Figs. 2 and 2A show the devices in the exchange VStA for outgoing trailic to the exchange YStB.

Fig. 3 shows the devices in the exchange VStB for incoming trailic from the exchange VStA and outgoing trailic to the exchange VStC.

Fig. 4 shows the devices in the exchanges VStC and VStD.

Fig. 5 shows the devices in the exchange VStA for trafiic to the exchange VStE and the devices in the latter exchange.

Figs. 6 and 7 show the circuits of the secondary switches, and

Fig. 8 an arrangement in which a temporary blocked signal is transmitted to the starting exchange.

I. BAsIo EsTABLIsHMEN'r oFfrHs CoNNEc'rroN As' PEB FIG. 1

Each exchange of the system has a definite characterizing number which has to be dlalled by the calling subscriber independent o! the exchange in the system to which the wanted 4subscriber belongs. The characterizing numbers for the exchanges VStA, VStB, VStC, VStD and VStE are the digits 2, 3, 4, 5 and 6 respectively.

From the exchange VStA towhichit will be assumed the calling subscriber Tnl is connected, the exchanges VStC and VStD can only be reached over the intermediate 'exchange VStB or the intermediate exchange VStE. The connecting path over the intermediate exchange VStB is preferably to be used. Only if this connecting path is inaccessible calls to the exchanges VStC and VStD are set up over the connecting path via exchange VStE.

'Ihe call from subscriber Tnl to the subo! the exchange VStD causes the connecting line VIA to be switched through to the secondary switch MWdS and thus to the group selector GWd3. The connection to the subscriber 5725 is completed by setting the group selector GWd3 on the seventh level and the nal selector on the ilitlrcontact of the second level.

Calls proceeding from the exchange VStA t the exchange VStE pass over the secondary switch MWaIB, the repeater UeA and the connecting lline VLB ai'ter the group selector GWaI has been set on the sixth level. The repeater UeA2 transmits the signal peculiar to the exchange VStE over the connecting line VLS and this causes the connecting line VL to be coupled with the group selector GWe3 in the incoming repeater UeEi. Through the transmission of the further numerical impulse trains in accordance with the wanted subscribers number, the connection is completed.

scriber 2355 connected to his own exchange VStA v is set up over the group selector GWai (second level) group selector GWa2 (third level) and the final selector LWa (fth level and fifth contact).

For establishing a connection to the subscriber 3764 who is connected to the exchange VStB, the group selector GWai is raised to the level 3 corresponding to the characterizing digit 3 for the exchange VStB and searches in this level for the approach to a free connecting line VLI associated with the exchange VStB. Other approaches to the connecting lines VLI which are also used for calls to the exchanges VStE and VStD may be reached over the levels 4 and 5 of the group selector GWai corresponding to the digits 4 and 5 of these exchanges. In each approach there is disposed a secondary switch which is preferably pre-set.

After the group selector GWal has been set,eA switching means become operative in the repeater UeAI of the connecting line VLI and t'ransmit a signal over the connecting line VLI which connects up the branch of the connecting line VLI which passes over the secondary switch MWb3 in the repeater UeBI in the exchange VStB. The secondary switch MWb3 is also preset. The subscriber Tn3164 is reached by the corresponding setting of the group selector GWb3 and a nal selector which is not shown.

A call to subscriber 5725 who isconnected to the exchange VStD is established. The group se Vso The progress of calls when there are no lines accessible between the two exchanges will now be considered.

A11 the connecting lines VLI between the exchanges VStA and VStB are blocked.

When the characterizing signal for this condition becomes eiTective the secondary switches MWa3, MWa4 and MWa5 are set on an overflow contact kl, lcl, and k5 respectively. To each overilow contact is connected an approach to connecting line VL5 leading to the exchange VStE. `In each of these approaches there is disposed a pre-set secondary switch for example in the approach reached over the overilow contacts k3 of the secondary switch MWIc3 and which characterizes the exchange VStB, the secondary switch MWaIIi; in the approach over the overflow contact kl of the secondary switch MWa4 which characterizes the exchange VStC, the: secondary switch MWail, and in the approach reached over the overow contact k and which is associated with the exchange VStD, the secondary switch MWaI5.

II with the connecting paths in this condition a call is initiated to the subscriber 3714 of the exchange VStB the calling subscriber is connected to the connecting line VL5 over the secondary switches MWa3, MWal3 and the repeater UeA2 after the group selector GWaI has been set. Through the transmission of the exchange characterising digit of the exchange VStB from the repeater UeA2 to the repeater UeEI, the secondary switch MWe3 in the latter is connected up. In the repeater UeE3 a signal is applied to the connecting line VLB leading to the exchange VStB which causes the switching through on to the secondary switch MWbI3 which stands on 1 the line to a free group selector GWb3.

lector GWaI is set on the fth level and seized l the approach to the connecting line VLI in which is connected the secondary switch MWa5. In the repeater UeAl a signal peculiar to thevexchange VStD is applied to the connecting line VLI. In repeater UeBI the approach to the connecting line VL! containing the secondary switch MWb5 is coupled with the connecting line VLI. Switchingmeans in the repeater UeB2 transmit the signal characterizing the exchange VStD over the outgoing connecting line VL3, this causing the connecting line VL3 to be connected via the secondary switch MWc5, to the connecting line VLI, in repeater UeCI. A calling impulse is now transmitted from the repeater UeC2 to the want- If when setting up a call to the subscriber Tn5125`of the exchange VStD all 4the connecting lines VStA and VStB are engaged, the calling subscriber Tnl is connected to the connecting line VIA over the secondary switches MWa5 and MWaIS and the repeater UeA2 after the group selector GWaI has been set on the fifth level. The signal characteristic of the exchange VStD is connected to the connecting line VLS in the repeater UeA2. This causes switching through to the repeater UeE2 in the repeater UeEI over the approach to the secondary switch MWeB associated with the exchange VStD.

It will be assumed that connecting lines V1.8 run directly from the exchange VStE to the exed exchange VStD and this in the repeater UeDl change VStD. In the repeater UeE2 a cali i A l initiating impulse is applied to the Vseized con necting line VLB and causes the switching through on to a free group selector GWdI in the exchange VStD.

It no connecting lines VL8 are provided between the exchanges VStE and VStD the repeater UeE2 is dispensed with. Calls to the exchange VStS from the exchange VStE are set up over the intermediate exchange VStC. The secondary switch MWe is then disposed in an approach (shown dotted) characterizing the exchange VStD, to the repeater UeE4 and thus to the connecting 'line VL'L In the repeater UeEl when this is seized over the secondary switch MWe5 the signal characteristic of the exchange VStD is applied to the connecting line VL1 wherebyswitching means-in the repeater UeC3 causes the line to be switched through to the secondary switch MWcI 5 and thus to the repeater UeC2. From the latter a call initiating impulse is transmitted to the exchange VStD over the connecting line VIA.

If connecting lines VLB are provided calls proceeding to the exchange VStD can be extended over the connecting path over the connecting lines VL1 and thus via the exchange VStC in the event of the lines VL8 being inaccessible. This can be brought about by the secondary switch MWe5 on being set on an overiiow contact seizing an approach to a connecting line VL1 in which is disposed a pre-set secondary switch in the same way as in the case of the outlets from the overflow contacts of the secondary switches MWa3, MWa4 and MWa5 in the proaches are connected to overiiow contacts.

If in the outgoing connecting paths from the exchange VStA which are` to be used in preference for calls to the exchange VStC and VStD over the intermediate exchange VStB therex are free connecting lines VLI available between the exchanges VStA and VStB but all the lines VL3 outgoing from the exchange VstB or the lines VL4 leading from the exchange VStC to VStD are inaccessible, connections to the exchanges VStC and VStD are immediately extended over a connecting path leading in another main traic direction over which the desired exchanges VStC and VStD also canbe reached without a connection being established to the exchange VStB. In the present case the connecting path in ques'e tion will be that over the exchange VStE.

All the connecting lines VL3 connecting the exchanges VStB and VStC are inaccessible.

Over the connecting line VLI or a signalling lead common to all the connecting lines VLI a blocked signal is transmitted from the .exchange VStB to the exchange VStA. The result of this is that switching means are iniluenced in the repeater UeAI and cause thesecondary` switches WMM and WMa5 to be set on overilow contacts kd' and c. Secondary switch MWa3 is not influenced since the connecting lines VLI are still accessible for calls to the exchange VStB so that a diversion o/f this trafc over the exchange VStE is not necessary. The establishment of calls to the exchanges VStC and VStD takes place in the same way as when the connecting lines VLI were busy.

'If when the connecting lines VLI-VLB are free all the connecting lines VL4 between exchanges VStC and 'VStD are inaccessible a blocked signal is transmitted from the exchange VStC to the exchange VStB and from this exchange to the exchange VStA. A special relay arranged in this exchange causes only the secondary switch MWa5 to be set on the overflow contact ki and thus on the approach to the connecting lines VL5 to the exchange VStE. The secondary switches MWa4 and MWa3 are not influenced by this blocked" signal. l

Calling subscribers ofthe exchange VStA can establish calls to the exchange VStD by way of auxiliary connecting path over the exchange VStE in the manner described above.

In a similar way tothe subscribers of the exchange VStA the subscribers of the other exchanges of the system can use outgoing connecting paths in other main trailic directions by using the devices shown in the exchange VStA in the event of the connecting lines in a particularAdirection being inaccessible irrespective of whether these are the lines proceeding from the subscribers own exchange or from an intermediate exchange over which the call is to be established.

It was assumed that for all calls to the exchanges VStC and VStD the connecting path over the intermediate exchange VStB was preferably to be used. The system can also be arranged so that calls to the exchange VStC preferably pass over the intermediate exchange VStB while for calls to the exchange VStD the connecting path passing over the intermediate exchange VStE is preferably to be used. In this case calls to the exchange VStC could be extended over the auxiliary path over the exchange VStE and calls to the exchange VStD over the auxiliary path over the exchange VStB. l

In a similar manner to that in which calls to subscribers of the exchanges reached over the connecting line VLI can be extended over the exchange VStE if all these lines are busy, so in the event of all the lines VLB being busy calls to the exchange VStE can be set up over the exchange VStB. In this case the secondary switch MWaIS would be set on an overflow contact on the reception of the ,blocked signal to which contact is connected an approach to connecting lines VLI characteristic of the exchange VStE.

II. CONNECTIONS BETWEEN THE SUBSCRIBER 'Inl (VStA) AND TN5725 (VStD) OVER THE EXCHANGE VStB (Fles. 2 AND 4) tacts 20o5, 3uav4, 41u15, Schl and negative. In

this circuit on accountv of the high resistance of Windng I of relay TaS, relay Ta5 does not' energze. Over contact 1ta5 the circuit of magnet DAS of switch MAS -is broken and at contact 8ta'5 the seizing circuit over the switch MWa5 and thus that for the connecting line VLI is prepared. When the test wiper of the group selector GWaI which is set on the fifth level by the first digit dialled by the subscriber, nds the secondary switch MWa5 when seeking for a free 'connecting line VLI, the testing circuit is completed over: positive, windings I and II oi relay Pl, wiper and contact in the group selector GWal, contact 8ta5, winding I of relay Ra5, contact 9ra5, winding II of relay Ra and negative. Both relays Pl andl Ra! energize; The relay Pl brings the group selector to rest in the known way, switches the speaking leads through and at contact lllpl short-circuits the high resistance winding I. Relay Ra closes its contact llra5 and then opens contact lra5. It switches the speaking leads through at contacts l2ra5 and l3ra5 and by opening contact sral disconnects winding II. In the circuit over positive contact lllpl, winding II of relay Pl, wiper and contact of' the group selector GWal, contact Stai, winding I of relay Ra5, contact llrai. winding I oi' relay T5, wiper and contact of the secondary switch MWa5, relay Ca5, contacts 2Ca5, 31ml, Quai and Schl set up on the closing or contact llra5, relay Ca5 energizes. It locks up at contact l4ca5 in a circuit passing over relay Chl and opens contact 2oo5. Relay Chl disconnects the free potential (negative), at contacts Schl whereby the testing relays Taliof all free secondary switches standing on the contact line VLI, i. e., for example the test relays Tal and Ta3 of the secondary switches MWal and MWa3 are deenergized. These secondary switches are pre-set on other free connecting lines VLI.

The repeater UeAl of the connecting line VLl has three approaches corresponding to the three exchanges VStB, VStC and VStD which can be reached over the connecting line VLI and to which different numbers are allottedas has appeared already from the description of Fig. 1. When one of these approaches is seized the connection is automatically switched through at the incoming end of the connecting line, in that direction which is characterized by the approach seized. For promoting this switching through alternating current of a particular frequency is temporarily connected in the repeater UeAl to the connecting line VLi. The connection takes place on the energizing of the seizing relay Ca associated with the approach seized. This characterizing current is disconnected by a relay Ch! which is slow-to-operate and which is connected up at contact l5chl by relay Chl.

Since in the present case the approach characterizing the exchange VStD was seized over .the secondary switch MWa5, the relay Ca5 by closing contact l6ca5 has connected the alternatng current source WQ in bridge across the leads of the connecting line VLI. We5.of the junction controlling device isy energized in the repeater UeBl in the exchange VStB, Fig. 3, by alternating current ilowing over the connecting line VKl and this switches on the switch-through relay Du5 at contact l'lwe5. The relays We3 and Wel do'not energize in response to the alternating current WQ5 characterizing the exchange VStD.

Before proceeding with the description of the further switching operations in the exchange VStB the switching operations in the exchange VStA- consequent `on the connection of the alternatingcurrent source WQS `will be explained:

On the energizingV of relay Ch! connected by the seizing auxiliary relayChl at contact l5chl, the source WQ! of alternating current is disconnected from the connectlngline VLI by the opening of contacts l8ch2- and l9ch2. The speaking leads are switched through at contacts 2llch2 and 2lch2.

After the speaking leads have been switched through in the group selector GWal and the sec- Only relay ondary switch MWa5 the bridge relay Al energizes in the known way over a bridge across the speak--l ing leads established at the impulse repeater in the .group selector GWal. It closes its contact 22al and thereby energizes the slow release relay Vl. leads of the connecting line VLI are finally switched through.

In the exchange VStB the switchthrough" relay Du5 connects the approach characterizing the exchange VStD to the connecting line VL3 in which the secondary switch MWb5 is disposed by closing contact 21du5. At contact 28du5 it prepares a locking circuit at contact 29du5 switches on the slow-to-energize relay Fb which on energizing disconnects the junction controlling device comprising relays We3, Wel and W by opening contacts llfb and Bljb, and switches the speaking leads through at contacts 32fb and 33fb. In the direct current circuit set up over the choke coil Drl (Fig. 2) the bridge relay A3 (Fig. 3) energizes and switches on the slow-release relay V3 which at contact 351:3 completes the locking circuit for relay Du5 prepared at contact 28du5. The speaking leads are switched through at contacts 3'la3 and 38a3.

The secondary switches (MWb5 and MWb4) in the exchange VStB are pre-set as those in the exchange VStA. Thus the secondary switch MWb5 for example is standing on the free connecting line VLB shown in the drawing. Relay Tb5 which holds the circuit of the rotary magnet D open at contact 39tb5 is energized over: positive, winding II of relay T125, contact 40rb5, winding I of relay T125, wiper and contact of the switch MWb5, relay C115, contacts 4lcb5 and 42ch3 and negative. In this circuit relay Cb! does not energize on account of the high resistance of winding II of relay Tb5. The seizing circuit of the secondary switch MWb5 is prepared at contact 43tb5 and is completed on the closing of contact 21du5; positive, contacts 2'ldu5, 43tb5, winding I of relay R125, contacts 44H75, winding II of relay Rb5 and negative. Relay R closes its contact l5rb5 and thereupon opens its contact 40rb5 and also contact 44rb5.

The speaking leads in the secondary winding switches MWb5 are switched through contacts 46H25 and 41rb5.

In the circuit over the low resistance windings I of relays Rb5 and Tb5 established at contact 45rb5, relay CD5 energizes, locks up in a circuit passing over relay Ch3, at contact 45cb5 and thereupon opens contact Ilcb5. Relay cH3 at contact l2ch3 breaks the testing circuits of all the other secondary switches standing on the seized connecting line VL3. These search for another free connecting line. Contact l9ch3 is closed for a purpose to be explained later. At contact 50cm relay Chl which is slow to operate is connected up.

Since the approach to the connecting line VL3 characterizing the exchange VStD was seized At contacts 23al and vl the speaking' witch M`Wc5. When the relay Fc pulls up its armature the junction controlling device with the relays Wel and Well is disconnected at contacts 54fc and 55fc, and at contacts 56fc and Slfc the speaking leads are switched through.

In the exchange VStB, Fig. 3, the source WQS of alternating current which was connected at contact 36cb5 is disconnected by the slow-tooperate relay Chl, which was operated on the operation of relay Ch3, by the opening of contacts 58chl and 59cm.

After the speaking leads have been switched through in therepeater UeCl at contacts 56fc and 5'lfc the bridge relay A4 is energized in the circuit passing over the choke-coil D12 in the repeater -UeDl. It switches on the slow release relay V5 at contact 60M and at contact Glad switches through the upper speaking lead. The lower speaking lead is switched through at contact 621:5.

Since the exchange VStD is the last in the source the preparatory transmission of a special exchange signal as occurs in the preceding exchanges through the temporary connectionof the alternating current source WQ5 is not necessary but may be used if calls are to be characterized in the same way at the terminal exchange as in the case of the intermediate exchanges.

In the present case it is arranged that a call initiating impulse is given to the exchange VStD by the establishment of a direct current bridge across the speaking leads of the connecting line VL4. This D. C. bridge contains the choke-coil Dr3 over which the bridge relay A5 in the repeater UeDl is energized after the connecting line VL3 has been switched through at contacts Blad and 62v5 in the repeater UeCI. The relay A5 initiates the switching operations necessary for the further establishment of the call.

When the calling subscriber Tnl transmits numerical impulses for setting the switches in the exchange VStD the impulses are extended by relay Al (Fig. 2) by means of contact 23al to relay A3 (Fig. 3) and from this by means of contact 31a?. to relay A4 (Fig. 4) and from this by means of contacts 6la4 to relay A5. Relay A5 controls the circuitserving to set the group selector GWd3 and the nal selector LWd.

In the arrangement shown the release of the connection and the restoration of the connecting lines used is dependent upon the calling subscriber Tnl. When this subscriber hangs up his receiver the circuit over relays Pl, Ra, Ta5, Ca5 and Chl is broken by the release relay (not shown) in the group selector GWal. Relay Ra5 breaks the speaking leads. Relays Al, A3, A4 and A5 release in succession and this results in the release of al1 the connecting devices in the exchange.

III. ESTAELISHMENT or CALLS PnocEEorNo FBoM THE EXCHANGE VStA WHEN CONNECTING LINES Ex- TENDING FROM AN INTERMEDIATE EXCHANGE ARE 'INAccEssrsLE 1. All connecting lines VL4 between the exchanges VStC and VStD blocked If all the connecting lines VL4 are blocked all the relays Ch5 (Fig. 4) are energized. VThe busy relay Br2 is operated over the serially arranged contacts lllch5, l lch5', etc., and applies negative potential to the overllow contacts of the secondary switches MWc5 and MWcE over contacts 'l2br2. All the free secondary switches in the 75 approaches to the connecting lines VIA set themselves on these overflow contacts.

Furthermore relay Br! closes contacts 'llbrZ and 'l5br2 and thereby connects the source WQ! o! alternating current to the leads of the connecting line VL3, for transmitting the blocking signal. This connection `occurs both in the'case of free and also in the case of engaged connecting lines.

In the previous exchange VStB in the connectlng path the relay Ubi connected in a bridge between the connecting line VL3 and earth is energized by the alternating current WQZ transmitted over the leads of the connecting line VL3 -ln parallel. Relay Ub5 by closing contacts '|6ub5 and 'l'lub5 connects a source WQZ of alternating current to the connecting line VLI In the exchange VStAv relay Uai energizes in responseto this alternating current and opens its contact 4ua5 in the approaches to all the connecting lines VLI which are characteristic 0f the exchange VStD. The result of this is that the circuits which are maintained by free secondary switches in the approaches to connecting lines VLI which are used on calls to the exchange VStD are broken. Thus the circuit over relay Ta5 of the secondary switch MWali is broken. It releases and completes the circuit for the rotary magnet Dai at contacts Tta5. The secondary switch MWaS operates until its test wiper reaches the` overflow contact 12105 to which negative potential is connected by contact 18ua5. Relay Ta5 then energizes over: positive. winding II of relay Ta5, contact lra5, winding I of relay Ta5, overow contact k5, contacts 'l8ua5, lead 19, relay Ral and negative.

Relay Ta5 energizes. The secondary switch is brought to rest through the opening of contact 'lta5. At contact Stai the seizure is prepared by a group selector CWal. l

In the secondary switch MWaI5 whose circuit corresponds to that of the secondary switch MWaS, relay Ral does not yet energize because the resistance of winding II of relay T115 is too great. I

The secondary switch MWal-5 on which the secondary vswitch MWa5 is now set lies in that approach to the connecting line VL5 which is to be used for calls to the exchange VStD.

If with the connecting path in this condition the subscriber Tnl wishes to set up such a call relay RaS is energized after the setting ofthe group selector GWa5. It switches the speaking leads through at contacts l2ra5 and l3ra5 and also the blocking lead at contact llra5. In the secondary switch MWal relay Ral energizes in the blocking circuit. It switches through both the speaking leads and the blocking lead (contacts not shown) and closes contact ral5 which lies in parallel with contact l8ua5 (Fig. 2). The result of the closing of this contact is that when a connecting line VL4 in the connecting path which is preferably to be used becomes free, and relay Ua5 releases, the connection established over the secondary switches MWuaS and MWualS inthe course of being established is not influenced.

In the repeater Uea2 relay Cal6 energizes in the blocking circuit. Through the cooperation vof relay Cal5, Ch6, Ch'l, the alternating current `ing connecting line VL5 via the secondary switch MWeI with the connecting line VLI leading to the exchange D. These operations correspond to those described for the establishment of the call over the intermediate exchange VStB so that a detailed description is not necessary at this point.

After the calling subscriber is connected to the exchange VStD the call is completed by the setting of the switches within this exchange.-

I! no direct connecting lines VL! are provided between the exchanges VStE and VStD the sec- -ondary switches MWeB are disposed in the exchange VStE (as indicated in dotted lines) in approaches to the connecting lines VL'I which lead to exchanges VStC. Any routing of calls to the exchange VStD over the exchange VStE then serves no purpose. Ii, however, in setting up the system connecting lines VLI are provided the routing of calls to the exchange VStD over the exchange VStE can be provided for from the start so that no considerable alteration to the system will later be necessary.

In this case when relay Uai becomes operative which relay characterizes the inaccessibility of the connecting lines VLI, the secondary switch MWal is seton overow contact. A connecting line VLB is not seized however since relay Uai also causes the secondary switch MWaIB to be set in the overiiow position Icll by the opening of contact Naai and the closing of contact luai. In the overilcw position ilk!! the busy signal is connected to the speaking leads and this the subscriber hears if he attempts .to set up a call to the exchange VStD. If later connecting lines VLB are provided the ability to establish calls from the exchange VStD to exchange VStE ls provided by simply shunting the contact Blua! and disconnecting negative potential from contact l2ua5.

It no contact lines VLB are provided between the exchanges VStD and VStE and it is not proposed to provide any later, itis, of course, necesits contact brl and libri. In the exchange VStA relay UA! energizes and opens the contacts in the approaches characterizing the exchange VStC and also in those approaches over which calls are established to the exchange VStD. This last is necessary because when all the connecting lines VLI are blocked no connection to the exchange VStD can be established over the preferred connecting path. Thus contact tual in the approach' over the secondary switch MWai and Slual in the approach over the secondary switch MWaI are open. The contacts 881ml and 891ml are closed and thus free potential is applied to the overflow contacts kS and kl of the secondary switches MWa5 and MWal. The secondary switches MWa5 and MWal step to the overflow position inI which the approaches to connecting lines VLS leading to the exchange VStE are connected.

The energization of relay Ual is not iniluenced on the secondary switch MWaI because calls to subscribers of the exchange VStB can still be set up.

If during the time in which the secondary switch MWa5 is in the overflow position on account of the connecting lines VL3 being busy the calling subscriber Tnl wishes to establish a call to the exchange VStD, he connects again to a free connecting line VLS over the secondary switches MWa5 and MWaI5, after dialling the characterizing digit 5. In the repeater UeA2 the source WQ5 of alternating current is temporarily connected up and influences the juncsary for the secondary switch MWa to be set` on an approach to a connecting line VLB when the connecting lines VLI become blocked and relay UaS energizes. As may be seen from Fig. 6 relay Ua5 in this case characterizes the special overilow contact kil as free by closing contact I'Iluai, the secondary switch becomes set on this overilow contact. because the relay Ua5 breaks its testing contact at contact luai as already described.

Ii' a call to the exchange VStD is initiated while the secondary switch MWaS is standing on the overilow contact kl, the calling subscriber immediately hears the busy signal after the connecting has been switched through at the group selector GWaI and at the secondary switch MWaI since the busy signal is applied to the speaking leads in this overilow position.

2. All connecting lines VL3 between exchanges VSB and VSC' blocked.

If all the connecting lines VLB between exchanges VStB and VStC are blocked the characterizing signal for the inaccessibility of the outgoing connecting lines VLI from the exchange VStC is transmitted over one of the connecting lines between the exchanges VStA and VStB for example the connecting line V1.2.

Since in this case the relays Chi in all thev tion controlling device (not shown) in the repeater UeEI. According as to whether connecting lines VLB are available or not the connection is either extended directly from the exchange AStE to AStD or via the intermediate exchange VStC.

If there are no connecting lines VLB provided the secondary switch MWaE possesses two overflow positions ki and k52 as shown in Fig. 6. As explained in the previous section the secondary switch is set in the overflow position k5l if calls to the exchange VStD cannot be established on account of all the lines being blocked. Over the overflow position k52 calls to the exchange VStD are extended over the exchanges VStE and VStC when the lines VL3 are busy. When relay Ual energizes the secondary switch MWa5 is brought to the .overflow position k52 by the opening of contact 3ua4 and the closing of contact Iual. To this overilow position an approach to the connecting line VL5 over the secondary switch M'Wal5 (Fig. 5) is connected. The establishment of a call to the exchange VStD then takes place in the manner described.

3. Inaccessibility of the connecting lines extending from an intermediate exchange in the auxiliary connecting path If when the connecting lines extending from an intermediate exchange in the preferred connecting path are engaged the secondary switches -in the starting exchanges'corresponding to this lines VLl and VL8 which lead from the exchange' Alternatively when the secondary switches are set on an auxiliary connecting path, one may' refrain from immediately controlling the secondary switches in the event of outgoing connecting lines `from an intermediate exchange in this connecting path being blocked, in the event of a further auxiliary path no longer being available. Assume that the secondary switch MWa stands on the approach to the connecting line VL5 on account of the connecting line V1.4 being blocked. All the connecting lines VL8 are blocked. A call to the exchange VStD is initiated and the calling subscriber is switched through to the secondary switch MWe5 in the approach to the connecting line V118 over GWal, MWa5, MWa|5, UeAZ, VIE and UeEl. Since all the lines VLB are blocked, relay B15 is energized and has closed the secondary switch MWeS i up over contact Hlm and contact Ilirali. At contact llm and Illm the device iniluenced by the busy signal and disposed between the speaking leads is disconnected. Relay M remains energized throughout the .duration of the call.

If before relay Th becomes operative busy signal is applied at a subsequent point in the 'connecting path, relay N energizes. It locks up lover its winding II at contact H611. and applies positive potential directly to winding I of relay Tal5 at contact Il'ln. It thus maintains the circuit over this relay independent of the potential applied over wiper H8. The thermo-relay Th is switched oil at contact. I09n. Contact H911 is opened. At contact |2011l the rotary magnet Dal5 Y is connected to the wiper standing on the contact segment Ill. forward until its wipers reach an overflow position in'which the lower wiper has left the contact segment ill. The secondary switch is brought to rest. Relay N releases since current no longer'flows overits winding II. Relay Tal5 and the relays in series with it are maintained energized over contact H911, wiper II8, overflow contact |20 and contact IZIraIS; the busy sigv nal is connected to the speaking leads in the overflow position. This the ycalling subscriber.

toy be set in the overflow position k53. In the overflow position iik53 the busy signalis connected to the speaking leads. The secondary switch MWaI5 in the exchange VStA can then be influenced by this busy signal so that it passes into an overflow position and releases the connecting path over the exchange UStE. Since the unnecessary seizure of the connecting path over VL5 to the exchange VStE only occupies a fraction of a second, this can be tolerated particularly ,seeing that the secondary switch MWaI5 only has toA pass into the overflowposition when it has been seized and not also when it is not seized when all the connecting lines VLB are blocked.

A circuit whereby the secondary switch MWaI 5 is able to be brought into the overflow position under the influence of the busy signal which is connected up in the overflow position of the switch MWe5 is shown in Fig. T.

The secondary switch is set in 'preparation on an approach to a free connecting line. Relay Tal5 is thus energized and has opened contact I 0ltaI5, and closed contact |02tal5. When the group selector GWal is set on the secondary switch MWa5 which occupies the overflow position ilk-5, relay Ra|5 is energized by current over .its two windings I and II. It closes contacts l3rai5, IMraIS, i05ral5, H5rai5 and |06ra|5 and opens contacts |01ra|5 and i08ra|5. The speaking leads are switched through as is also the seizing lead.

A device which can be influenced by a busy signal is bridged across the speaking leads in the secondary switch. This device includes a relay N which is energized when the busy signal is applied at a succeeding point in the connecting path. It is disconnected if a busy signal is not applied within a definite period after the secondary switch has been seized. For this purpose a sloW-to-operate relay is' provided. This may be a thermo-relay Th which is connected up over contact I|l6ra|5 and the contact segment III when the secondary switch MWaIS is seized. Ify

the busy signal is not applied within the heating period of the thermo-relay, relay Th energizes and switches on relay M at contact ||3th which locks hears. After the receiver has been replaced; relays PI, Rai, Ta5, Ral and Talrelease. The secondary switches' are set afresh on a free outgoing line.

The devices which become operative when the busy signal is applied and which include the 4winding I of relay N can also be arranged in the connecting line seized by the secondary switch. Relay N would then energize a controlling relay in the secondary switch on energizing and the secondary switch would be started up and be brought torest in the overflow position.

As previously described a characteristic signal n for the blockage of a group of connecting lines is transmitted over one of theconnecting lines during the time that the blocking is effective. The system can be so arranged that when all outgoing connecting lines are blocked and .one subsequently becomes free, temporary potential is connected to the connecting line over which the signalling is to take place.

Such an arrangement is shown in Fig. 8. The devices of the exchange VStA and VStB are only shown in so far as they are necessary. The relay Ual which controls the secondary switches MWa4 and MWa5 when the connecting lines VL3 are inaccessibleY is not connected to the connecting line VL2 but in a local circuit. The repeating relay Ual' is consequently connected to the connecting lines.

When relay Bri which is operated in the exchange VStB when all the connectinglines V1.3 are blocked pulls up its armature it switches on the relay An (winding I) over contact 200brl. At contacts 20mm and 202an the source-WQZ of alternatingcurrentis connected in parallel to the two leads of the connecting line VL2. For disconnecting the source WQZ of alternating current the slow-to-energize and slow-to-release Vrelay Anh is connected' up at contact; 203an, and

Secondary switch is switched the circuit over winding I of relay An is broken the relay releases and by opening contacts 20|an and 202ml disconnects the source WQ2 of altere nating current from theconnecting line VL2.

For indicating the blocked condition of the outgoing onnecting lines VLB the source of alternating current is only applied temporarily to the connecting line VL2. The current flowing over this line operates the relay Ua!' which is connected in a bridge between the speaking leads and earth in the exchange VStA and by closing its contact 201ua4' switches on winding I of relay Ua!: positive, contact 208ML relay Ua!, (winding I) contact 201ua4' and negative. Relay Ua! energizes and controls the secondary switch in the manner described. At contact 209ml! it prepares a circuit which will be explained later.

When relay Ua!' releases after the disconnection of the alternating current in the exchange VStB the following circuit is established: positive, contact 2081111, winding I of'relay Ua!, contact 2I0ua!, winding I of relay Hr!, contact 209ha! and negative. Relay Ua! remains energized and relay H1- energizes. The latter closes at contact 2| Ihr! and then opens its contact 208ML The following locking circuit is now set up: positive,

contact 2l |hr!, winding II of relays Hr! and Ua!,

contact 209ml! and negative. v

When the connecting lines V1.3 become free relay Br in the exchange VStB releases, contact 20Ibrl is open and'contact 2l2brl is closed, winding II of relay An is switched on over positive contacts 2l2brl and 20611119, windingI of relay An and negative. By closing contacts -ZIlIan and 202ml relay An connects the source WQ2 of a1- ternating current in parallel to the speaking leads of the connecting lines VL3 for transmitting a signal characterizing the free condition of the connecting lines VLB.

When contact 2001211 opens, the locking circuit for relay Anh is broken. Relay Anh makes a delayed release and among others opens its contact 206mm. Relay An is thus disconnected and releases. By opening contacts 20mn and 2U2an it disconnects the source WQ of alternating current from. the -connecting line VL2.

In the exchange VStA relay Ua!' energizes in response to the alternating current flowing over the connecting line VL2 on account of the release of relay Bri. Contacts 201ua!' and 2I3ua!' are closed. Winding II of relay Ua! is consequently short-circuited at contact 2I3ua!'. Relay Ua! cannot remain energized over its windings I because contact 298m! is open. Relay Ua! thus releases and thereby causes the secondary switches such as MWaS and MWa! to be set again on approaches to connecting lines in the connecting path which is`preferably to be used.

When relay Ua!' releases on account of the disconnection of the alternating current from the connecting line VL2 in the exchange VStB, contacts 201ua4 and 2I3ua!' are opened. Contact 2|0ua!' is closed. Since relay Ua! has already released and accordingly contact 209ml! is open, current no longer flows over one of the windings of relay Hr!. This therefore releases and opens contact 2| Ihr! and closes its contact 2087111. c

The devices for receiving temporary signals indicate the blockage of all the connecting lines VL3 reached over the intermediate 'exchange VStB or the relays of one or more of'\them is now once more in the rest condition.

When the signal characterizing the blockage of all the connecting lines VL! from the exchange VStC which is disposed beyond the intermediate exchange VStB is to be transmitted to the exchange VStB, this signal can be extended to the exchange VStA in that the relay Ub5 (not shown) which is disposed in the exchange VStB and is energized temporarily like relay Ua!' in the exchange VStA connects the source WQ! of alternating current to the connecting line VLI provided Ifor transmitting this signal at contacts 11125 and llliubi and thereby controls the receiving devices in the connecting line VLI in the exchange VStA in the same manner. as already de- Y scribed. These receiving devices are then controlled in the same way when outgoing connectline common to all the connecting lines. A separate signalling line may be provided for each signal or alternatively a single signalling line can be provided for all signals in that the currents used are of different types such as direct current and alternating current or alternating currents of` differing frequencies.

What is claimed is: 1. In a telephone system, a pair of exchanges interconnected by trunk lines, means in one of said exchanges operated responsive to all of said trunk lines becoming busy, a distant exchange, and means in said distant exchange operated responsive to the operation of said last means.

2. In a telephone system, a pair of exchanges interconnected by trunk lines, a third exchange, means associated with said trunk lines and effective to transmit a signal to the third exchange responsive to all of said trunk lines becoming busy.

3. In a telephone system, a pair of exchanges interconnected by a group of trunk lilies, a third exchange, means associated with said group of trunk lines and effective to signal transitorily to said third exchange responsive to an all-trunksbusy condition thereof, means in the third exchange operated by said transitory signalling and maintained operated after the cessation thereof,

said rst means thereafter eiiective responsive to the cessation of said all-trunks-busy condition to signal transitorily to said third exchange to restore said last means.

4. In a telephone system wherein calls from a first exchange to a second exchange are extended through an intermediate exchange over trunklines, means for making any of said trunk lines busy, means effective if all cf the trunk lines between the intermediate exchange and the second exchange are busy to transmit an all-trunks=busy signal to the rst exchange over a trunk line extending from the first exchange to the intermediate exchange, said last means transmitting said signal over said last trunk line regardless of whether said last trunk line is busy or id1e.

5. In a telephone system wherein connections from a local exchange to a distant exchange are extended over a predetermined route including one or more tandem exchanges, means in the local exchange individual to each group of interexaaeaass change are received, a plurality of groups ofy trunks over which calls outgoing from said exchange may be extended, means individual to each group of said plurality of groups of trunks, said means operated responsive to an al1-trunksbusy condition of the corresponding group and effective to revert a `signal from said exchange over a trunk of said first group.

'7. In a telephone system, a plurality of serially related exchanges, means for extending a call from the rst exchange of the series to any other desired exchange of the series through those exchanges of said series which intervene between said rst and said desired exchange, means associated with the trunk lines joining each pair of adjacent exchanges in said series and operated when none of the trunk lines between that pair of exchanges is available, and means controlled by said last means to indicate at all times in said first exchange whether or not a trunk line between each pair of exchanges in said series is available.

8. In a telephone system, a plurality of serially related exchanges, means for extending calls over idle trunk lines from the first exchange of said series to any other desired exchange of the series through those exchanges of the series which intervene between said rst and said desired exchange, and means for preventing the partial extension of those calls which cannot be completed to the desired exchange because of the unavailability of idle trunk lines beyond some one of said intervening exchanges through which the call would pass.

9. In a telephone system wherein calls from subscribers in an originating exchange to subscribers in a terminating exchange are extended through an intermediate exchange over trunk lines, means effective if none of the trunk lines between the intermediate exchange and the terminating exchange are available to prevent a trunk line from the originating exchange to the intermediate evchange from being seized for a call from said originating exchange to said terminating exchange.

10. In a telephone system wherein calls from subscribers in an originating exchange to subscribers in a terminating exchange are extended through a plurality of intervening exchanges in series over trunk lines, means eiective if none of i the trunk lines extending from the last intervencludes a plurality of serially related intervening exchanges, means effective when all of the trunks outgoing over said predetermined route from any one of the intervening exchanges arebusy to prevent any trunk incoming from said first exchange to the first intervening exchange of said series from being seized for the extension of a connection to said second exchange.

13. In a telephone system, a plurality of serially related exchanges, means for extending a call from the first exchange of the series to any other desired exchange of the series through those exchanges of said series which intervene between said ilrst and said desired exchange, means associated with the trunk lines joining each pair of adjacent exchanges in said series and operated when none of the trunk lines between that pair of exchanges is available, and means, controlled by said last means for preventing the partial extension of those calls from said first exchange which cannot be completed to the desired exchange because of the unavailability of trunks beyond some one of said intervening exchange through which said call would pass.

14. A telephone system as claimed in lclaim 13, having an exchange not in said series over which calls may be extended to said desired exchange, wherein said last means routes calls to the desired exchange over said last exchange when some portion of the route through said series of exchanges is unavailable.

15. In a telephone system `wherein connections from a first exchange to a second exchange may be extended over a preferred route or an alternative route, a tandem exchange included in said preferred route, and change-over means in the rst exchange operated to render the alternative route effective responsive to all trunks outgoing from the tandem exchange in said preferred route becoming busy.

16. In a telephone system wherein calls from subscribers in an originating exchange to subscribers in a terminating exchange may be exlng exchange of said series to the terminating excludes one or more tandem exchanges, means.

tended over a preferred route or an alternative route, said preferred route including one or more tandem exchanges, means effective if said calls cannot be completed over the preferred route due to the unavailability of trunks outgoing in the preferred route from one of said tandem exchanges to direct said calls over the alternative route without rst attempting to extend same over said preferred route.

17. In a telephone system, two exchanges. means for extending connections from the rst to the second of said exchanges over either of two groups of trunks outgoing from said first exchange, one or more tandem exchanges through which must be completed those connections extended from said first exchange over the rst of said groups of outgoing trunks, and routing means in the rst exchange operated responsive to all of the trunks outgoing from any of said tandem exchanges toward the second exchange becoming busy, said routing means effective to direct the extension of connections from the iirst to the second exchange over the second of said groups of trunks outgoing from the first exchange.

18. In a telephone system, a trunk for extending callsin any of a plurality of trail'ic directions, a plurality of approaches having access to said trunk, each approach corresponding to one of said tralc directions, and means responsive to a be extended over a predetermined route which intraillc direction becoming impassable to calls for 'blocking only that approach to said trunk which corresponding to one of said groups of trunks,

and means responsive to an all-trunks-busy condition of any of said groups for blocking the approach corresponding to that lgroup.

20. In a telephone system, a plurality of serially related exchanges, means for extending a call from the first exchange of the series to any other desired exchange of the series through those exchanges of said series which intervene between said rst and said desired exchange, a plurality of approaches, in said rst exchange, to the trunk lines between said iirst exchange and the second exchange ofsaid series, each approach corresponding to one of the exchanges of said series to which calls from the first exchange may be extended, and means responsive to any exchange of said series becoming inaccessible due to all of the trunks extending thereto from the next preceding exchange of said series becoming busy ior blocking, in said first exchange, both the approach corresponding to said inaccessible exchange and the approaches corresponding to all exchanges of the series to which calls must be extended via vthe inaccessible exchange, the approaches corresponding to exchanges between said first exchange and said inaccessible exchange remaining unblocked to permit the extension of calls thereto. 21. In a telephone system, a pair of exchanges interconnected by trunk lines, means associated with said trunk lines and operated responsive to all of said trunk lines becoming busy, a third exchange, and means controlled by saig last means to indicate at all times in said third exchange whether or not all of said trunk lines are busy.

22. In a telephone system, two exchanges interconnected by trunk lines, a third exchange, a device in the third exchange, and means associated with said trunk lines effective' to operate said device in one way whenever al1 of said trunk lines are busy and to operate said device in a different way whenever at least one of said trunk lines is not busy.

ALFRED KEYSER.

WALTER PINEIL. 

